<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    body {
      display: flex;
      flex-wrap: wrap
    }
    [class|=content] {
      height: 100px;
      text-align: center;
      line-height: 100px;
    }
    @media screen and (max-width: 600px) {
      [class|=content] {
        width:100%;
        font-size: 1em
      }
    }
    @media screen and (min-width: 600px) {
      [class|=content] {
        width: 50%;
        font-size: 1.5em
      }
    }
    @media screen and (min-width: 900px) {
      [class|=content] {
        width: 25%;
        font-size: 2em
      }
    }
    .content-1 {
      background-color: aqua;
    }
    .content-2 {
      background-color: black;
    }
    .content-3 {
      background-color: gray;
    }
    .content-4 {
      background-color: blue;
    }
  </style>
</head>
<body>
  <div class="content-1">
    hello world
  </div>
  <div class="content-2">
    hello world
  </div>
  <div class="content-3">
    hello world
  </div>
  <div class="content-4">
    hello world
  </div>
</body>
</html>